FIG. 7 is a sectional view illustrating an non-energizing state of a conventional normally closed type three-way solenoid valve.
In FIG. 7, a bobbin 1 is a formed resin inserted with a plate 22 made of a magnetic material, and terminals 6 and 7, provided with a coil winding section 1g. Further, the bobbin 1 is provided with an input port 2, an output port 3 and a discharge port 4, and has O-ring grooves 1a and 1b receiving O-rings 9 and 10 for preventing oil leakage.
A plunger 29 is made of a magnetic material, guided by the bobbin 1 and vertically slidably arranged. A bush 23 is made of a magnetic material, and inserted on one end side of the bobbin 1 so as not to be in contact with the plunger 29. Further, a case 11 is made of a magnetic material, attached to the outer periphery of the bobbin 1 having a coil 12 wound on the coil winding section 1g, and is secured to the plate 22 by caulking. A holder 24 made of a magnetic material is provided between the case 11 and the bush 23, and ensures magnetic association of the two. A non-magnetic holder 25 is attached to the one end side of the bobbin 1 so as to secure internal parts of the solenoid.
A ball 13 is inserted into the input port 2 at the other end of the bobbin 1, and further a bush 14 is inserted therein. Going off of the ball 13 is prevented by heat-caulking a caulking section 1c of the bobbin. The plunger 29 is provided integrally with a valve rod 29a for pushing the ball 13 attached to the input port 2, and the base portion of the valve rod 29a forms a valve section 29b.
A magnetic circuit is formed with the case 11, the plate 22, the plunger 29, the bush 23 and the holder 24.
In the conventional solenoid valve 100 having the configuration described above, in a non-energizing state of the coil 12, the ball 13 is seated onto a valve seat 1e under a pressure of a fluid acting on the input port 2, and the fluid does not flow in from the input port 12. Movement of the ball 13 seated onto the valve seat 1e pushes up the valve rod 29a. As a result of upward movement of this valve rod 29a, i.e., the plunger 29, the valve section 29b leaves a valve seat 1d, and communication is established between the output port 3 and the discharge port 4.
When energizing the coil 12, magnetism is supplied to the magnetic circuit composed of the case 11, the plate 22, the plunger 29, the bush 23 and the holder 24, and the plunger 29 is magnetically attracted toward the plate 22. This magnetic attraction overcomes the pressure of the fluid acting via the ball 13 and the plunger 29, and the plunger 29 moves toward the plate 22. Under the effect of this movement of the plunger 29, the valve section 29b is seated onto the valve seat 1d, and at the same time, the valve rod 29a of the plunger 29 pushes the ball 13. The ball 13 thus leaves the valve seat 1e. The output port 3 is thus separated from the discharge port 4, and there is achieved communication between the input port 2 and the output port 3.
In the conventional solenoid valve 100, a portion generating an electromagnetic force and a valve portion controlling the fluid are integrally configured. It is therefore impossible to achieve common parts among solenoid valves of different specifications, leading to a higher cost.